FRAMINGHAM – Elizabeth Warren peered over the edge of a trench where workers were lowering a sewer line into the mud and listened intently as a man in a hard hat extolled the sweeping benefits of better plumbing promised by the $22 million project.

A day later, Senator Scott Brown showed up just 3 miles away, donned his own hard hat — labeled “Senator Brown” — and handed doughnuts and coffee to workers installing drywall in a partially constructed Framingham bank.

While the Senate rivals wrapped themselves in lunch pail imagery last week, the job sites they visited spoke to a larger point they are trying to make about the role of government in helping to create jobs.

Brown, with his “Thank You for Building This” tour of local businesses, is emphasizing the role of the private sector in fueling the economy. Warren, with her “Rebuild Now” tour of public works projects, is highlighting how government support for roads, bridges, and rails can power an economic revival.

“We don’t know what the next great business is going to be,” Warren, a Democrat, declared at the sewer project on Thursday. “But we’re pretty sure they’re going to need roads and bridges to be able to get their goods to market. We’re pretty sure they’re going to need water and sewer to keep their operations going.”

On Friday, 23 hours after Warren’s event, Brown greeted workers who are building NorthEast Community Bank.

“It’s not a government-created job that’s going to get us out of this economic mess,” said Brown, a Republican. “It’s people like this who are working very hard to create small-business jobs.”

Brown’s tour has an added edge.

He wants to lash Warren to President Obama’s statement last month that “if you’ve got a business — you didn’t build that; somebody else made that happen.” The president was reiterating a theme central to Warren’s campaign, that infrastructure lays the groundwork for businesses to thrive.

But Republicans have seized on Obama’s phrasing to portray Democrats as hostile to private enterprise. Late last month, Mitt Romney, who employs the same political strategists as Brown, launched a “We Did Build This” tour to praise business owners for their ingenuity.

Warren’s tour is built around her proposal to spend $100 billion on roads, bridges, and schools. The Harvard Law School professor is also promoting the plan with a television ad that shows cranes and construction projects in China juxtaposed with crumbling roads and bridges in this country.

“China invests 9 percent of its GDP in infrastructure,” Warren says in the ad. “America? We’re at just 2.4 percent. We can do better.”

Brown says that if the United States were to spend 9 percent of its gross domestic product on infrastructure, it would cost $1 trillion annually. He likens Warren’s plan to Obama’s $789 billion stimulus program, which is being hammered by negative ads from the Romney campaign and the Republican National Committee.

“She’s comparing us to China, and actually wants us to do another stimulus bill,” Brown said. “The first one didn’t work, and led to higher unemployment. And where are we going to find the money?”

Warren emphatically rejects any suggestion that her plan is a stimulus program.

“This is about building,” she said. “That’s the heart of what this is about and, in fact, that’s all this is about it.”

The “Rebuild Now” plan will not add to the debt, she says. It will be paid for entirely by repealing $39 billion in tax breaks for oil companies, letting the Bush tax cuts expire for those earning more than $250,000 a year, and eliminating $50 billion in direct agriculture subsidies, among other measures, she said.

“This is about making smart choices,” Warren said. “This is about deciding not to put money into the oil industry and instead putting money into upgrading our infrastructure so that our businesses will be able to grow and flourish.”

The Brown campaign has pounced on Warren’s focus on China by e-mailing articles from conservatives who have criticized the ad. “Negative reviews continue to roll in on Elizabeth Warren’s ‘be more like communist China!’ campaign ad,” the Brown campaign wrote in one e-mail.

Warren said the comparison to China is valid.

“China is a warning,” she said. “If China is making investments in state-of-the-art infrastructure while the US lets roads and bridges crumble, lets water and sewer systems collapse, then our businesses can’t compete.”

Warren’s plan calls for $50 billion in new spending on highway, rail, and aviation projects — including $850 million in Massachusetts, which she says would create 11,000 jobs in the state.

About $30 billion would be spent to modernize schools and community colleges, which Warren says would create 4,900 jobs in Massachusetts. The plan also calls for expanding broadband Internet access, reinstating tax breaks for commuters who use public transit, a national infrastructure bank, and more flexibility for states to spend federal highway funds.

At the sewer project on Thursday, Warren nodded enthusiastically as a worker told her three pump stations were being replaced and the sewer lines would eventually be covered by bike trails.